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Archived

Avalanche Forecast

Mar 11th, 2013–Mar 12th, 2013
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Purcells.

Forecasted amounts of precipitation spatially vary in the region. This forecast reflects areas that will receive the most amounts; possibly the East and South part of the region.

Confidence

Fair - Forecast snowfall amounts are uncertain for the entire period

Weather Forecast

Monday Night and Tuesday: The first of a series of systems approaching the interior is expected to start spreading precipitation over the region early Tuesday. Light to moderate precipitation amounts (more on the Eastern part of the region) are expected with strong SW winds . Freezing level will start rising to reach around 1600 m. and will stay high for the rest of the period.Wednesday: Precipitation easing off but still some moisture available. Winds are forecasted to be strong to extreme from the SW. Temperatures staying warm and freezing levels up to 1900 m. in the S part of the region. Thursday: Another burst of precipitation is expected with similar freezing levels and lighter winds switching from the SW.

Avalanche Summary

A couple natural slab avalanche size 2.5 were reported on W and SW slopes one of which was triggered by a loose avalanche. 

Snowpack Summary

Up to 5 cm of new snow is covering a variety of surfaces; a 2 cm thick suncrust on SE-S-SW facing slopes at all elevation, a melt-freeze crust all the way up to 1600 m. and some well developed surface hoar on shaded slopes above that elevation. The forecasted precipitation and warm temperatures will add a significant load to the snowpack (possibly from 20 to 50 mm in water equivalent until Thursday). I suspect that the variety of surfaces described previously will become gradually more reactive as the load add up starting tomorrow. This could also awake the 60-90 cm deep persistent surface hoar layer that has been less reactive to skier traffic lately creating a potential for very large avalanches.

Avalanche Problems

Storm Slabs

Precipitation and warm temps are expected in the days to come creating new storm slabs at all elevations and new wind slabs lee of strong SW winds in the alpine and treeline. The potential avalanche size is expected to increase as more snow piles up.
Watch for clues of instability like whumphing and cracking in the snow.>Make conservative terrain choices during periods of heavy loading from new snow, wind, or rain.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 4

Persistent Slabs

Persistent weak layers exist buried down 60-90 cm, comprising of surface hoar and a sun crust. It could be triggered by the forecasted precipitation and warm temperatures.
Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 6